Sn Tn n Sn/Tn=2n-3/4-3 a3/b5+b7+a3/b4+b8
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SnTnnSn/Tn=2n-3/4-3a3/b5+b7+a3/b4+b8SnTnnSn/Tn=2n-3/4-3a3/b5+b7+a3/b4+b8SnTnnSn/Tn=2n-3/4-3a3/b5+b7+
Sn Tn n Sn/Tn=2n-3/4-3 a3/b5+b7+a3/b4+b8
Sn Tn n Sn/Tn=2n-3/4-3 a3/b5+b7+a3/b4+b8
Sn Tn n Sn/Tn=2n-3/4-3 a3/b5+b7+a3/b4+b8
前n项和公式为：Sn=na1+n(n-1)d/2 （即二次函数形式）
故设：Sn= (2n--3) x kn ； Tn= (4n--3) x kn (k ≠0)；
所以 Sn= 2kn^2 --3kn ；Tn=4kn^2 --3kn
所以：S6= 72k --18k= 64k ,S5= 50k--15k=45k ；则 a6=1/2(a3+a9)=S6--S5 =19k 即：a3+a9=38k
T6=144k--18k=126k,T5=100k--15k=85k；则b6 =1/2(b5+b7)=1/2(b4+b8)=T6--T5=41k
即：(b5+b7)=(b4+b8)=82k
所以：a9/(b5+b7)+a3/(b4+b8)= （a3+a9）/(b5+b7) =38k/82k= 19/41
Sn Tn n Sn/Tn=2n-3/4-3 a3/b5+b7+a3/b4+b8
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